Frequency-domain equalization of single carrier transmissions over doubly selective channels

by 1976- Liu, Hong

Abstract (Summary)

Wireless communication systems targeting at broadband and mobile transmissions
commonly face the challenge of fading channels that are both time and frequency
selective. Therefore, design of effective equalization and estimation algorithms for
such channels becomes a fundamental problem. Although multi-carrier transmissions
demonstrate prominent potential to combat doubly selective fading, several factors
may retard their applications, such as: high peak-to-average power ratio, sensitivity
to phase noise, etc. Meanwhile, single-carrier transmission is a conventional approach
and has important applications, such as HDTV broadcasting, underwater acoustic
communication. In this dissertation, we focus on receiver design for single-carrier
transmissions. Our goal is to design and develop a group of channel estimation
and equalization algorithms in the frequency-domain, which enable high performance
and low complexity reception of single-carrier transmissions through doubly selective
channels.
For single-carrier transmissions over moderately fast fading channels with longdelay
spread, we present an improved iterative frequency-domain equalization (IFDE)
algorithm based on soft-interference-cancellation (SIC) and propose a novel adaptive
frequency-domain channel estimation (AFDCE) based on soft-input Kalman filter,
where soft information feedback from the IFDE can be exploited in the channel
estimator. Simulation results show that, compared to other existing schemes, the
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proposed scheme offers lower MSE in channel prediction, lower BER after decoding,
and robustness to non-stationary channels.
We extend the IFDE/AFDCE scheme to accommodate the application of digital
television (DTV) signal reception. Compared with the traditional joint decision
feedback equalization (DFE) /decoding plus frequency-domain least-mean-square
(FDLMS) channel estimation approach, the proposed scheme achieves better performance
at a fraction of the implementation cost.
For very fast fading large-delay-spread channels, traditional FDE methods fail,
because channel variation within a FFT block induces significant off-main-diagonal
coefficients in the frequency domain. To conquer the problem, we apply Doppler
channel shortening to shape the energy distribution of those coefficients and derive a
pilot-aided MMSE estimator to estimate them for SIC. We also propose a novel IFDE
by leveraging both the sparse structure of shortened channel and finite-alphabet property
of transmitted symbols. Numerical results show that the proposed scheme has
advantages over the well-known FIR-MMSE-DFE/RLS-CE scheme in both performance
and complexity.
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To my family
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